1. Field of the Invention
The present invention relates to methods of preparing microcapsules and resin particles, as well as microcapsules and resin particles, and more particularly, it relates to methods of preparing microcapsules and resin particles in nonaqueous media, and microcapsules and resin particles having fine particle sizes.
2. Description of the Background Art
Microcapsules which are capable of internally containing various materials are utilized in various fields. In general, such microcapsules are prepared by two types of methods, i.e., physical/mechanical methods and chemical methods. Depending on the usage, microcapsules of fine particle sizes may be required. However, it is difficult to prepare such microcapsules of fine particle sizes by physical/mechanical methods, and hence the same are prepared by chemical methods. Coacervation, interfacial polymerization and in situ method are known as such chemical methods.
In specific fields which are related to recording materials, medical materials and coating materials, ultrafine microcapsules of the so-called submicron order having particle sizes of not more than 1 .mu.m may be required. However, such microcapsules of not more than 1 .mu.m in particle size are not industrially prepared in general, and methods for preparing the same are not known in the art either. Japanese Patent Laying-Open No. 63-232840 (1988) discloses a method of preparing microcapsules having particle sizes of not more than 0.5 .mu.m by dispersing a polymer compound in the presence of a surface-active agent. However, this method is adapted to prepare a wall of microcapsules by adding a liquid phase to a solution in which a polymer compound is dissolved to separate the polymer, through dissolution and separation of the polymer. Therefore, the microcapsules as obtained are disadvantageously inferior in solvent resistance, for example.
On the other hand, Japanese Patent Laying-Open No. 3-221137 (1991) discloses a method of dispersing a hydrophobic material for serving as a core material in an organic phase in which self-dispersible resin having diisocyanate group is dissolved and adding an aqueous solution in which diamine etc. is dissolved thereto, for instantaneously obtaining fine particles in the water medium and forming microcapsule walls. According to this method, however, the fine particles are obtained in the water and hence the material to be contained in the microcapsules is limited to that which is slightly soluble or insoluble in the water. According to this method, further, the fine particles and the microcapsule walls are instantaneously formed and hence the capsulating states, particle sizes and particle size distribution of the microcapsules as obtained are remarkably influenced by the conditions for mixing the organic phase and the aqueous solution. In addition, this gazette describes that it is extremely difficult to obtain ultrafine capsules of the submicron order.
As hereinabove described, there is no method of preparing microcapsules having fine particle sizes of not more than 1 .mu.m in a nonaqueous medium in general, and hence it is generally impossible to prepare microcapsules having particle sizes of the submicron order with cores of a water soluble material.